While the manufacture and various uses of polyolefin-based fiber, webs and corresponding nonwoven materials are well known in the textile art, attempts to broadly apply such knowledge to produce products in the area of personal hygiene, such as cover stocks for catamenial devices, disposable diapers, incontinence pads and the like, have met with somewhat limited success.
In general, such products must have a fluid-absorbent core, usually comprising one or more layers of absorbent material such as wood pulp, rayon, gauze, tissue or the like, and, in some cases, synthetic hydrophilic material such as a polyurethane foam.
The fluid-absorbing product is generally provided in the form of a thermally bonded pad, of wood pulp, fiber and/or conjugate fiber, which may have a rectangular or somewhat oval shape. To protect clothing, and surrounding areas from being stained or wetted by fluids absorbed in the pad, it is generally backed by a fluid-impervious barrier sheet.
To enhance a sense of comfort, such absorbent core generally also has a facing of cover stock material which masks at least the body-facing surface of the product. The purpose of this cover is two-fold, namely (1) to help to structurally contain the loosely packed core of absorbent material and (2) to protect the wearer from continuous direct contact with moisture from previously wetted absorbent material. The facing or cover stock must, therefore, be pervious to fluids on the side of the product that is placed against the body, actively promoting the immediate transfer of each fluid application or insult directly into the absorbent core, and yet itself be essentially nonabsorbent. It is also necessary to minimize lateral migration of fluid along the cover stock surface even after repeated insults, and for the surface to continue to feel smooth and soft to the touch. Certain additional characteristics are also sometimes desired, such as visual opacity plus specific coloring or luster on the outer surfaces and the acceptance of designs.
In order to obtain many of the above-listed characteristics, however, it is imperative that cover stocks utilizing essentially hydrophobic polymeric material such as polyolefins, be made relatively hydrophilic and have the above-noted continuing ability to pass aqueous fluids through to an absorbent core, even after several insults (i.e. wettings) without wash out or leach out of hydrophilic-promoting agents. This is particularly important, in the case of diaper cover stock, to avoid lateral liquid migration and side leakage, and to minimize any interference with fabric bonding steps which would cause a reduction in wet strength of the final product.
Based on prior teaching in the paper-making art, it is known that short term hydrophilicity can be imparted to essentially hydrophobic polymers such as polyolefin fiber by using flash evaporation techniques and treating the resulting fiber or filament with hydrophilizing agents such as polyvinyl alcohol or various nitrogen-containing water-soluble polymers (ref. U.S. Pat. Nos. 4,156,628, 4,035,229, 4,082,730, 4,154,647, 4,156,628, 4,035,229, 4,273,892 and 4,578,414).
For personal hygiene purposes, however, a general lack of resistance to wash out among most art-recognized hydrophilic-promoting additives, plus interference with web-bonding properties justifies continuing efforts to improve long term hydrophilicity. Such efforts have, more recently included incorporating alkoxylated alkylphenols or corresponding polyoxyalkylenes into spun melt compositions (ref. U.S. Pat. No. 4,578,414). Serious high speed spinning, bonding, and fluid retention problems remain, however.
It is an object of the present invention to more effectively utilize inert hydrophobic polyolefin-containing nonwoven materials in the area of personal hygiene.
It is a further object of the present invention to efficiently utilize polyolefin-containing webs comprised of one or more of fiber, and fibrillated film within cover stock.
It is a still further object to obtain and retain hydrophilicity and liquid strike through properties in strong well bonded nonwoven hydrophobic materials utilizing polyolefin component.